On Sat, Aug 2, 2014 at 1:35 PM, David Wilson <[email protected]> wrote:
> > Repeated list and str concatenation both have quadratic O(N**2) > > performance, but people frequently build up strings with + > > join() isn't preferable in cases where it damages readability while > simultaneously providing zero or negative performance benefit, such as > when concatenating a few short strings, e.g. while adding a prefix to a > filename. > Good point -- I was trying to make the point about .join() vs + for strings in an intro python class last year, and made the mistake of having the students test the performance. You need to concatenate a LOT of strings to see any difference at all -- I know that O() of algorithms is unavoidable, but between efficient python optimizations and a an apparently good memory allocator, it's really a practical non-issue. > Although it's true that join() is automatically the safer option, and > especially when dealing with user supplied data, the net harm caused by > teaching rote and ceremony seems far less desirable compared to fixing a > trivial slowdown in a script, if that slowdown ever became apparent. > and it rarely would. Blocking sum( some_strings) because it _might_ have poor performance seems awfully pedantic. As a long-time numpy user, I think sum(a_long_list_of_numbers) has pathetically bad performance, but I wouldn't block it! -Chris -- Christopher Barker, Ph.D. Oceanographer Emergency Response Division NOAA/NOS/OR&R (206) 526-6959 voice 7600 Sand Point Way NE (206) 526-6329 fax Seattle, WA 98115 (206) 526-6317 main reception [email protected]
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